NOD2 is a protein, also known as the caspase recruitment domain family, member 15 (CARD15), which plays an important role in the immune system. It is an intracellular pattern recognition receptor, which is similar in structure to resistant proteins of plants and recognizes molecules containing the specific structure called muramyl dipeptide (MDP) that is found in certain bacteria. This gene is a member of the NOD1/Apaf-1 family and encodes a protein with two caspase recruitment domains (CARDs) and eleven leucine-rich repeats (LRRs). The protein is primarily expressed in the peripheral blood leukocytes. It plays a role in the immune response by recognizing the bacterial molecules which possess the muramyl dipeptide (MDP) moiety and activating the NF-κB protein.